Free downloads - theschoolrun.com has lots of free downloadable activity sheets
We recommend Cosmic Yoga - https://www.youtube.com/user/CosmicKidsYoga
Khan Academy - https://www.khanacademy.org - especially good for maths and computing for all ages but other subjects at Secondary level. Note this uses the U.S. grade system, but it's mostly common material.
BBC Learning - http://www.bbc.co.uk/learning/coursesearch/ - this site is old and no longer updated and yet there's so much still available, from language learning to BBC Bitesize for revision. No TV licence required except for content on BBC iPlayer.
Futurelearn - https://www.futurelearn.com - free to access 100s of courses, only pay to upgrade if you need a certificate in your name (own account from age 14+ but younger learners can use a parent account).
Seneca - https://www.senecalearning.com - for those revising at GCSE or A level, tons of free revision content. Paid access to higher level material.
Open Learn - https://www.open.edu/openlearn/ - free taster courses aimed at those considering Open University, but everyone can access it. Adult level, but some e.g. nature and environment courses could well be of interest to young people.
Blockly - https://blockly.games - learn computer programming skills - fun and free.
Scratch - https://scratch.mit.edu/explore/projects/games/ - creative computer programming.
Ted Ed - https://ed.ted.com - all sorts of engaging educational videos.
National Geographic Kids - https://www.natgeokids.com/uk/ - activities and quizzes for younger kids.
Duolingo - https://www.duolingo.com - learn languages for free. Web or app.
Mystery Science - https://mysteryscience.com - free science lessons
The Kids Should See This - https://thekidshouldseethis.com - wide range of cool educational videos
Crash Course - https://thecrashcourse.com - subject videos on You Tube
Crash Course Kids - https://m.youtube.com/user/crashcoursekids - as above for a younger audience
Crest Awards - https://www.crestawards.org - science awards you can complete from home.
iDEA Awards - https://idea.org.uk - digital enterprise award scheme you can complete online.
Paw Print Badges - https://www.pawprintbadges.co.uk - free challenge packs and other downloads. Many activities can be completed indoors. Badges cost but are optional.
Tinkercad - https://www.tinkercad.com - all kinds of making.
Prodigy Maths - https://www.prodigygame.com - in U.S. grades, but good for UK Primary age.
Cbeebies Radio - https://www.bbc.co.uk/cbeebies/radio - listening activities for the younger ones.
Nature Detectives - https://naturedetectives.woodlandtrust.org.uk/naturedetectives/ - a lot of these can be done in a garden, or if you can get to a remote forest location!
British Council - https://www.britishcouncil.org/school-resources/find - resources for English language learning.
Oxford Owl for Home - https://www.oxfordowl.co.uk/for-home/ - lots of free resources for Primary age.
Big History Project - https://www.bighistoryproject.com/home - aimed at Secondary age. Multi disciplinary activities.
Geography Games - https://world-geography-games.com/world.html - geography gaming!
Blue Peter Badges - https://www.bbc.co.uk/cbbc/joinin/about-blue-peter-badges
The Artful Parent - https://www.facebook.com/artfulparent/ - good, free art activities.
Red Ted Art - https://www.redtedart.com - easy arts and crafts for little ones.
The Imagination Tree - https://theimaginationtree.com - creative art and craft activities for the very youngest.
Toy Theater - https://toytheater.com/ - educational online games.
DK Find Out - https://www.dkfindout.com/uk/?fbclid=IwAR2wJdpSJSeITf4do6aPhff8A3tAktnmpaxqZbkgudD49l71ep8-sjXmrac - activities and quizzes.
Maths Frame - https://mathsframe.co.uk/ - hundreds of interactive maths games, and lots of worksheets linked to the new curriculum. All resources are designed by an experienced KS2 teacher. New games and worksheets are added regularly.